The present invention relates to a wet etching station and a wet etching method adapted for utilizing the same. More particularly, it relates to a wet etching station and a wet etching method adapted to utilizing the same, which can uniformly etch a large-diameter wafer by taking advantage of differences in wet etching rates caused by an intentional non-uniform temperature distribution in the etching bath.
The high integration of semiconductor devices onto integrated circuits with increased capability requirements has led to smaller individual devices on larger chips. This, combined with the desire to reduce cost and increase productivity yields for semiconductor device fabrication, has promoted the use of large-diameter wafers. Such large-diameter wafers require greater process uniformity controls, since uniformity is a critical consideration when employing the larger wafers in semiconductor devices.
Therefore, it is essential to ensure an adequate process uniformity when handling a large-diameter wafer in a wet etching station. Such uniformity is indispensable to wet etching (or cleaning) in semiconductor device manufacturing. Wet etching generally proceeds with a group of wafers (a "batch") in a single run by contacting the batch with a bath containing a chemical etchant. In such a process, the etching rate is affected to a considerable extent by the temperature of the chemical etchant. Therefore, the chemical etchant is continuously circulated in the bath to keep its temperature uniform throughout the bath with the goal of ultimately obtaining a uniform etch-rate across an entire wafer.
A conventional wet-etching station will be described in detail with reference to FIG. 1.
In the prior art, the temperature of a chemical etchant 3 is to be kept uniform in the hope that the surface of a wafer 1 can be uniformly etched by being immersed in a bath 5 for wet-etching, wherein the bath contains a chemical etchant. To maintain such a uniform temperature, the chemical etchant 3 in the bath 5 needs to be constantly circulated by using a pump 7, which is regulated by a constant-temperature controller 9.
In the conventional wet etching station, when the wafer is immersed in the chemical etchant to perform an etching process, the lower portion of the wafer comes into contact with the chemical etchant earlier than the upper portion thereof. Also, when the etched wafer is taken out the upper portion of the wafer is exposed to the air earlier than is the lower portion thereof. Thus, during the wet etching, the lower portion of the wafer is in contact with the chemical etchant longer than any other portion thereof, resulting in that portion being etched longest. Likewise, the upper portion is etched for a correspondingly shorter time than any other portion of the wafer.
As is apparent from the above discussion, the wafer is not etched uniformly in the conventional etching batch process. This problem becomes especially serious when a large-diameter wafer is being produced to provide the high integration demanded for currently used semiconductor devices. As a result, the uniformity of the pattern formation is poor. This leads to variations in characteristics of the semiconductor device depending upon the chip location on the wafer.
Further, the reliability of an insulating layer is degraded because it does not have a uniformity of thickness across the entire wafer.